The effect of high pressure-low temperature treatment on physicochemical properties in milk

This study was carried out to investigate the effect of high pressure-low temperature (HPLT) treatment on physicochemical properties and nutrients in milk. The milk was treated at 200 MPa and −4°C for 10, 20, and 30 min. Protease and lipase activities of HPLT-treated milk were highly inactivated compared with that of raw milk. Among time treatments, the 30-min treatment showed the lowest activities compared with others. Absorbance of thiobarbituric acid increased with time in HLPT-treated milks; however, no difference was observed between the raw milk and milk treated for 10 min. The concentrations of short-chain fatty acids except C₄ in HPLT-treated milks increased with time. The total free amino acids in HPLT-treated milks were greater than that of the raw milk for the 30-min treatment. l-Ascorbic acid, niacin, and riboflavin in HPLT-treated milks were significantly lower compared with concentrations in raw milk. For color, the L-value of HPLT-treated milks was significantly lower than that of the raw milk; however, there was no difference in the a-value for 10 min and in the b-value at 20 min between the raw milk and the HPLT-treated milks.     

Influence of the frozen storage period on the coagulation properties of caprine milk

Coagulation properties of caprine milk frozen for up to 60 days at −27 °C were investigated using a rheometer with a vane geometry tool. Coagulation time (CT) and aggregation rate (AR) were estimated during gel formation for 64 min at 1 Hz and 1% strain. Evaluation of curd firmness (CF) was done using frequency spectra of the resulting gels. The data were processed by ANOVA and linear regression (with frozen storage time as independent variable and pH, AR, CT and CF as dependent variables). No statistically significant changes in coagulation properties were found, although the milk pH decreased from 6.64 (non-frozen pasteurised milk) to 6.41 after 60 days of frozen storage. The results of this research showed that the coagulation properties of caprine milk were not significantly altered during 60 days frozen storage. It could be assumed, therefore, that the cheese-making processing properties of caprine milk would also not change.     

Effect of frozen storage on the proteolytic and rheological properties of soft caprine milk cheese

Freezing and long-term frozen storage had minimal impact on the rheology and proteolysis of soft cheese made from caprine milk. Plain soft cheeses were obtained from a grade A goat dairy in Georgia and received 4 storage treatments: fresh refrigerated control (C), aged at 4°C for 28 d; frozen control (FC), stored at −20°C for 2 d before being thawed and aged in the same way as C cheese; and 3-mo frozen (3MF), or 6-mo frozen (6MF), stored at −20°C for 3 or 6 mo before being thawed and aged. Soft cheeses had fragile textures that showed minimal change after freezing or over 28 d of aging at 4°C. The only exceptions were the FC cheeses, which, after frozen storage and aging for 1 d at 4°C, were significantly softer than the other cheeses, and less chewy than the other frozen cheeses. Moreover, after 28 d of aging at 4°C, the FC cheeses tended to have the lowest viscoelastic values. Slight variation was noted in protein distribution among the storage treatment, although no significant proteolysis occurred during refrigerated aging. The creation and removal of ice crystals in the cheese matrix and the limited proteolysis of the caseins showed only slight impact on cheese texture, suggesting that frozen storage of soft cheeses may be possible for year-round supply with minimal loss of textural quality.     

Effect of storage at 4 degrees C on the physicochemical and renneting properties of milk: a comparison of caprine, ovine and bovine milks

The effects of cold storage at 4 degrees C for 12, 24 and 48 h on the physicochemical characteristics and renneting properties of ewes', goats' and cows' milks were compared. The most important changes were observed in cows' milk. Soluble calcium concentrations were not affected in ewes' milk but were increased by 10% in cows' milk and 7% in goats' milk. More casein was dissociated on cooling cows' (+300%) than goats' (+100%) milk, and there was no change in soluble casein in ewes' milk. The coagulation characteristics of cows' milk were more impaired by cold storage than goats' or ewes' milks. Coagulation times increased by approximately 30% and whey draining capacity decreased by 40% after cows' milk was cooled, but there were no changes with ewes' milk and only a slight decrease in coagulation time with goats' milk. We propose an interpretation of these results based on the physicochemical properties of each type of milk.     

Effect of preparation and storage of khoa on physicochemical properties of milk fat

The changes in milk fat during the preparation and storage of khoa were studied in three different seasons. Milk fat was extracted from the samples with chloroform using Soxhlet extraction. The solvent was evaporated using a vacuum evaporator followed by nitrogen flushing. The extracted fat samples were analysed for Reichert–Meissl, Polenske, saponification and iodine values, butyro‐refractometer reading at 40 °C and free fatty acids (FFAs). The study revealed an increase in the FFA content during conversion and storage of khoa, while there were small changes in other physicochemical properties of milk fat during the preparation of khoa from raw milk and its subsequent storage at room temperature.     

贮藏温度对青方腐乳生物胺和理化性质的影响

以市售的青方腐乳为原料,研究了开盖后贮藏在不同温度下其生物胺含量、水分活度（Aw）、pH值、氨基酸态氮的动态变化,探讨了生物胺与理化指标之间的相关性。结果显示,青方腐乳在不同温度下贮藏至15 d时总生物胺含量＞1 000 mg/kg,且组胺含量＞100 mg/kg,酪胺含量在贮藏至30 d时（除25 ℃第30天）＞100 mg/kg,均超过了相关标准推荐的限量值;在不同贮藏温度下,青方腐乳水分活度＞0.8,pH变化规律基本一致,在第15天达到最大,4 ℃贮藏时,氨基酸态氮含量随贮藏时间的延长而增大。相关性分析结果表明,理化指标的变化与生物胺存在一定的关系,pH与苯乙胺、尸胺、组胺和亚精胺呈极显著正相关（P＜0.01）。结果表明,为了食用安全,腐乳开盖后应尽量在15 d内食用完。     

Combined effects of freezing rate, storage temperature and time on bread dough and baking properties

This study compares the effects of freezing temperature and rate as well as storage temperature and time on the quality of frozen dough. Yeasted bread dough was frozen using four freezing rates (19-69 °C/h), then stored at −10, −20, −30, or −35 °C for up to 180 days. Dough strength diminished with longer storage time and higher storage temperatures. Cryo-SEM showed that dough stored at −30 and −35 °C had the least damaged gluten network. NMR studies showed that more rapidly frozen dough, and that stored at lower temperatures had lower transverse relaxation (T₂) times (9-10 ms). However, dough stored at −20 °C displayed the highest yeast activity among samples. Bread loaf volume decreased with storage time, and bread made from dough stored at −20 °C showed the highest loaf volume. Breads produced from −30 and −35 °C stored dough displayed less change in the texture profile during storage as well as less change in T₂ values. Response surface analysis showed that optimal properties occurred at freezing rates of around 19-41 °C/h and storage temperatures of −15 to −20 °C.     

Processing effects on physicochemical properties of creams formulated with modified milk fat

Type of thermal process [high temperature, short time pasteurization (HTST) or ultra-high temperature pasteurization (UHT)] and homogenization sequence (before or after pasteurization) were examined for influence on the physicochemical properties of natural cream (20% milk fat) and creams formulated with 20% low-melt, fractionated butteroil emulsified with skim milk, or buttermilk and butter-derived aqueous phase. Homogenization sequence influenced physicochemical makeup of the creams. Creams homogenized before pasteurization contained more milk fat surface material, higher phospholipid levels, and less protein at the milk fat interface than creams homogenized after pasteurization. Phosphodiesterase I activity was higher (relative to protein on lipid globule surface) when cream was homogenized before pasteurization. Creams formulated with skim milk and modified milk fat had relatively more phospholipid adsorbed at the milk fat interface. Ultra-high-temperature-pasteurized natural and reformulated creams were higher in viscosity at all shear rates investigated compared with HTST-pasteurized creams. High-temperature, short time-pasteurized natural cream was more viscous than HTST-pasteurized reformulated creams at most shear rates investigated. High-temperature, short time-pasteurized creams had better emulsion stability than UHT-pasteurized creams. Cream formulated with buttermilk had creaming stability most comparable to natural cream, and cream formulated with skim milk and modified butteroil was least stable to creaming. Most creams feathered in a pH range of 5.00 to 5.20, indicating that they were moderately stable to slightly unstable emulsions. All processing sequences yielded creams within sensory specifications with the exception of treatments homogenized before UHT pasteurization and skim milk formulations homogenized after UHT pasteurization.     

超高压微射流处理对火龙果汁微生物指标及理化特性的影响

目的 研究不同超高压微射流处理条件对火龙果汁品质和安全性的影响。方法 火龙果汁分别采用100、150和200MPa的超高压微射流处理1次和2次,测定不同处理条件下火龙果汁理化指标(平均粒径、总酸、可溶性固形物含量、总酚和花青素含量)和微生物指标(菌落总数、大肠菌群和酵母菌)。 结果 果汁的平均粒径、总酸含量、可溶性固形物含量随压力的增加而减小,总酚含量随压力的增加变化差异不显著,花青素含量随压力的增加先减少后增加;相同压力下,处理次数对平均粒径、总酸含量、可溶性固形物含量和总酚含量的影响不显著,100MPa下花青素的含量随处理次数增加而降低,但150、200MPa下花青素的含量随处理次数增加而增加;菌落总数、大肠菌群和酵母菌的数量均随着压力和处理次数的增加而减少。结论 超高压微射流处理能够对火龙果汁的理化特性产生影响,并且能够有效杀灭火龙果汁中的微生物,最终实现火龙果汁品质和安全的控制。     

Effect of salt concentration and temperature of storage water on the physicochemical properties of fish proteins

Biochemical and physical properties of fish proteins from damaged (filleted and skinned) and undamaged (free of trauma or broken skin) Pacific whiting were investigated during chilling in various salt concentrations at 0.7 to ?1.1 °C. The increase of pH and moisture content were suppressed when chilling water contained higher concentration of NaCl. Conductivities of damaged fish were maximal after 24 h storage, but those of undamaged fish continuously increased throughout 72 h. K-values increased, but rapidly increased at lower salt concentrations. Puncture force and deformation were very low when chilled water contained higher concentration of salt (2–3 g/100 ml). Gel colors were also negatively affected as the concentration of salt increased for chilling water. Our study suggest Pacific whiting may be stored at 0–2 °C, but at 0–1 g/100 ml salt concentration.     

羊乳与牛乳理化特性比较

以莎能奶山羊羊乳为样品,利用乳样自动分析仪,氨基酸自动分析仪、等离子发射光谱、色谱分析对其基本成分、氨基酸组成及含量进行了分析和检测,并与牛乳理化特性进行比较,为科学合理地利用羊乳,生产具有独特功能的羊乳制品提供了理论依据。     

烟熏火腿理化及贮存特性的研究

研究了烟熏火腿的理化及贮存特性,成品火腿具有低pH(平均值5·94)及高含水量(平均水分活度0·943)的特点,在0~4℃条件下,经过21d贮藏,细菌总数达2·5×103cfu/g;而在25℃条件下,经过21d贮藏,细菌总数达1·9×104cfu/g,火腿的保质期大大缩短。两种贮藏条件下,产品的pH值变化不明显。     

Some properties of set yoghurt made from caprine milk and bovine–caprine milk mixtures fortified by ultrafiltration or the addition of skim milk powder

Set yoghurt was produced from caprine milk (A), 70% caprine-30% bovine (B) and 50% caprine–50% bovine milk (C) mixtures, and stored for 14 days at ±4°C. Two methods of fortification, namely ultrafiltration (UF) and the addition of bovine skim milk powder (SMP), were applied to the milk mixtures. Some chemical, physical, microbiological and sensory properties of the six samples were analysed on the 1st, 7th and 14th days of storage. The effects of milk type, concentration method and storage period on the physicochemical and microbiological properties of the samples were investigated statistically.     

动态高压微射流处理对方竹笋膳食纤维理化及结构特性的影响

以方竹笋中提取的膳食纤维为研究对象,采用动态高压微射流（dynamic high-pressure micro-fluidization, DHPM）在不同压力条件（0,50,100,150,200 MPa）下进行处理,探究其对竹笋膳食纤维（bamboo shoots dietary fiber, BSDF）理化和结构特性的影响。结果表明,随着处理压力的增大,BSDF粒径先增大后减小,当处理压力为150 MPa时,粒径最小,为（370±11） nm,此条件下BSDF的持水力、持油力和膨胀力达到最大,较对照组分别提高了47.74%,50.54%,61.27%,且差异显著（P<0.05）。红外光谱分析表明DHPM处理不会改变BSDF的官能团,但会使BSDF内部的部分氢键断裂和半纤维素、木质素等发生降解;X射线衍射和热重分析表明DHPM处理不会引起BSDF的晶体结构改变,但晶体有序度会下降,进而导致其热稳定性降低;微观结构分析显示DHPM处理会使BSDF颗粒尺寸减小、表面粗糙、组织松散,且当处理压力为200 MPa时,颗粒发生团聚。综上,DHPM可以有效改善BSDF的理化性质,在膳食纤维改性方面具有一定的应用价值。     

湿热处理温度对多孔淀粉理化性质的影响

目的:研究湿热处理温度对多孔淀粉理化性质的影响。方法:将湿热处理温度分别控制在110、115和120℃,在水分含量为15%条件下湿热处理1 h,研究在该条件下湿热处理对多孔淀粉结构和性质的影响。结果:在水浴温度为85℃条件下多孔淀粉溶解度随湿热处理温度的增加而增加,膨胀度随着湿热处理温度的增加而下降;多孔淀粉吸油率随湿热处理温度的升高而增加;多孔淀粉糊的透光率随湿热处理温度的升高而下降,淀粉糊冻融稳定性、起始糊化温度和热糊稳定性随着湿热处理温度的升高而增强,糊化峰值粘度随湿热处理温度的升高而降低;湿热处理温度对多孔淀粉的结晶结构影响不大,多孔淀粉依然为A型结晶结构,随处理温度的升高其结晶度略有降低;当湿热处理温度为115℃时,其抗性淀粉含量最高,达27.67%。结论:湿热处理温度对多孔淀粉理化性质有明显影响,且随着湿热处理温度的不同存在差异性。      

低温储藏条件对大豆分离蛋白膜理化特性的影响

以大豆分离蛋白为原料制得可食性膜,研究在不同低温储藏条件下其功能特性,包括机械性能和阻隔性能的变化。结果显示:随冷藏温度的升高,其功能特性变化较为缓慢。而随冻藏温度的降低,断裂延伸率下降尤为明显,抗拉强度和脂质阻隔能力变化趋势次之,水蒸气透过率升高缓慢。冷藏时间与断裂延伸率呈显著正相关(p<0.05)。冷藏时间与水蒸气透过率和油脂渗透系数均呈极显著正相关(p<0.01)。冻藏时间与水蒸气透过率和油脂渗透系数呈显著正相关(p<0.05)和极显著正相关(p<0.01)。     

Combination treatment of high-pressure and CaCl2 for the reduction of sodium content in chicken meat batters: effects on physicochemical properties and sensory characteristics

A combination of high-pressure processing (HPP, 200 MPa, 10 min) and CaCl₂ (0.2%, w/w) on the cooking loss (CL), expressible moisture (EM), textural properties (hardness, springiness, cohesiveness, chewiness and firmness) and sensory attributes of reduced-sodium (1.25% NaCl) chicken meat batters (RCMB) was investigated. The results revealed that combining HPP with CaCl₂ significantly decreased EM, elevated sensory properties and acted synergistically in reducing CL and improving hardness, chewiness and firmness, which enabled RCMB to obtain quality characteristics similar to those with high salt (2.5% NaCl) content. These changes brought about by combined HPP and CaCl₂ could be attributed to increased apparent viscosity and proportion of immobilised water, enhanced rheological (elastic) properties and a denser, homogeneous protein gel network with evenly dispersed small fat globules. It is interesting to take advantage of the synergy between moderate HPP and low concentrations of CaCl₂ to develop meat products with reduced sodium content.     

贮存温度和贮存时间对复原乳稳定性的影响

研究了贮存温度和贮存时间对复原乳的pH值、流变特性、粒径、乳析率和离心沉淀率的影响,在此基础上分析了贮存过程中乳浊液粒径与乳析率、离心沉淀率之间的相关性。结果表明:随着贮存温度的升高,复原乳的pH值与表观黏度逐渐降低,而随着贮存时间的延长,二者均先升高后降低,其中25℃和37℃下贮存在第15天时达到最大值,而55℃下贮存在第7天时达最大值;贮存过程中乳浊液顶部粒径d4,3与乳析率有较好的相关性(P<0.05),二者均随着贮存温度的升高和贮存时间的延长而增大;贮存过程中乳浊液底部粒径d4,3与离心沉淀率有很好的相关性(P<0.05),二者随着贮存温度的升高先增大后减小,在37℃时达最大值,随着贮存时间的延长均有所增大。